It is already known that benzimidazole derivatives chlorinated in the 2 position can be prepared by reacting the corresponding 2-bromo-imidazoles with hydrogen chloride (cf. WO-A 97-06171). Thus, for example by treating 2-bromo-6,6-difluoro-[1,3]dioxolo-[4,5-f]benzimidazole with hydrogen chloride in the presence of dimethylformamide, 2-chloro-6,6-difluoro-[1,3]dioxolo-[4,5-f]-benzimidazole is obtained. However, this process has the disadvantage that the desired products are obtained in relatively low yields.
Furthermore, it is already known that 2-chloro-benzimidazole can be prepared by reacting 1,3-dihydro-benzimidazol-2-one with phosphorus oxychloride in the presence of hydrogen chloride (cf. J. Chem. Soc. 1963, 2930). However, corresponding chlorinations of 1,3-dihydro-benzimidazol-2-ones which contain a further fused-on heterocyclic ring on the benzene ring have hitherto not been described.